I bought a mirror star cruiser today so I could use the mirror material on my standard assault cruiser (they have the same physical configuration and ship class parts at the tailor).
I was thinking of getting the assault cruiser refit (regent class) eventually for this character. My character is mirror universe themed and I went to the ship tailor to see if the mirror material can be used on the Regent class parts before I made a final decision on whether or not I will buy the ship later.
Well the mirror material can be used on the Regent class parts but it is completely missing from 1 of the nacelles when you have all ship parts set to Regent. 1 nacelle has the type 6 material while the rest of the ship has the mirror material. This seems to be the same for any of the nacelles (Majestic, Sovereign, Noble, Regent) I choose in the advanced tab; 1 is missing the mirror material. When I click the dropdown for the nacelles and put my mouse over 1 type, both nacelles are missing the mirror material until I make a selection, then only the 1 is missing the material.
After fiddling around with it I think I found what causes it. In the screenshots you can see I have the Regent template highlighted on the far left side. This only happens if the Regent template is selected. I can select any of the other ship class templates and manually select the Regent parts in the advanced tab and the mirror material covers that nacelle.
Example: Here you can see I have the Majestic template on the far left selected but manually set all ship parts to Regent in the advanced tab on the right and both nacelles now have the mirror hull material covering them instead of just the 1. http://imageshack.us/a/img38/539/d5um.jpg
Edit: Also if you manually set the ship parts to Regent in the advanced tab without selecting a template on the left first, everything is fine.